On 11/13/2015 09:22 AM, Frederic Weisbecker wrote:
The tick dependency is evaluated on every IRQ. This is a batch of checks which determine whether it is safe to stop the tick or not. These checks are often split in many details: posix cpu timers, scheduler, sched clock, perf events. Each of which are made of smaller details: posix cpu timer involves checking process wide timers then thread wide timers. Perf involves checking freq events then more per cpu details.Checking these details asynchronously every time we update the full dynticks state bring avoidable overhead and a messy layout. Lets introduce instead tick dependency masks: one for system wide dependency (unstable sched clock), one for CPU wide dependency (sched, perf), and task/signal level dependencies. The subsystems are responsible of setting and clearing their dependency through a set of APIs that will take care of concurrent dependency mask modifications and kick targets to restart the relevant CPU tick whenever needed. This new dependency engine stays beside the old one until all subsystems having a tick dependency are converted to it. +void tick_nohz_set_dep_cpu(enum tick_dependency_bit bit, int cpu) +{ + unsigned long prev; + struct tick_sched *ts; + + ts = per_cpu_ptr(&tick_cpu_sched, cpu); + + prev = fetch_or(&ts->tick_dependency, BIT_MASK(bit)); + if (!prev) { + preempt_disable(); + /* Perf needs local kick that is NMI safe */ + if (cpu == smp_processor_id()) { + tick_nohz_full_kick(); + } else { + /* Remote irq work not NMI-safe */ + WARN_ON_ONCE(in_nmi());
Better to say "if (!WARN_ON_ONCE(in_nmi()))" here instead so we don't actually try to kick if we are in an NMI? -- Chris Metcalf, EZChip Semiconductor http://www.ezchip.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
